1. Field of the Invention
The present invention relates to a method for displaying a measurement of eccentricity in an optical system. More particularly at least one exemplary embodiment relates to displaying, analysis of and improving the eccentricity in a multi-lens system.
2. Description of the Related Art
Conventional methods for measuring eccentricity can be summarized with respect to (e.g. Yoshiya MATSUI and Masayuki USUI, Kougakukei no Henshin Sokutei ni Tsuite [Measurement of Eccentricity in an Optical System], Optical and Electro-Optical Engineering Contact, vol. 13, No. 11, pp. 11-20) three approaches associated with particular lenses and measurement techniques as:
(1) A method associated with measuring eccentricity while rotating a lens;
(2) A method associated with multiply reflected light rays used in the measurement of a Stationary lens; and
(3) A method associated with an Image rotator measurement of a Stationary lens.
All of these approaches project an indicator to a position of an apparent center of curvature of a surface to be measured by autocollimation and calculate the amount of eccentricity on the basis of a state (amounts of shift and displacement) of a reflected image from the surface with respect to a measuring reference axis.
Approach (1) measures eccentricity while rotating the lens to be measured. Approach (1) has an advantage that it can realize high-precision measurement in a simple structure, but has a disadvantage that it cannot accurately measure eccentricity for a lens system to be measured containing a movable unit, like a zoom lens. A lens system containing a movable unit requires a minute clearance around a sliding portion for moving the movable unit. Therefore, a process of measuring eccentricity while rotating a lens system to be measured, varies the weighted position of the lens, thus changing a state of eccentricity.
Approach (2) utilizes light rays that have made multiple passes between half mirrors and the lens to be measured. Approach (2), does not rotate the lens to be measured, so it can measure eccentricity of a lens system containing a movable unit. However, since the measuring light rays pass through half mirrors as much as six times, a loss of light intensity is a serious problem (e.g. Japanese Patent Publication No. 3-054287).
Approach (3) can measure eccentricity without rotating a lens system to be measured by utilizing an image rotator. In addition, since the number of times light passing through a half mirror is small, a loss of light is small. Propositions with this approach are disclosed in, for example, Japanese Patent Publication Nos. 51-009620, 7-081931, and 7-039982, and Japanese Patent No. 2621119.
A further lens eccentricity measurement system measures (e.g. Japanese Patent Laid-Open No. 4-190130) eccentricity by relatively moving an autocollimation optical system and the lens to be measured.
In the conventional systems described there is no specific proposition disclosed as to a method for analyzing a result of measurement of eccentricity and a method for displaying it.
Measurement of eccentricity of an optical system is aimed originally at analyzing what element is eccentric in a lens system to be measured and how eccentricity is present in the element and at obtaining effective information to deal with an eccentricity problem. In measurement of eccentricity of the system, even if the eccentricity of each surface of the lens system to be measured is accurately measured, displaying a result of measurement of eccentricity of each surface as only a numerical value is insufficient for readily determining a state of eccentricity and obtaining effective information to address an eccentricity problem.
This is because there are various definitions of coordinate systems (e.g., a rectangular coordinate system, a polar coordinate system, the orientation of coordinate axes, and the position of the origin) for a parallel eccentric component and a slope eccentric component in the amount of eccentricity, both the components being required for displaying numerical values indicating a state of eccentricity, and numerical values for one state of eccentricity may vary depending on a selected definition. Additionally, even if a selected definition is explicitly pointed out, it is difficult for one of ordinary skill to accurately and readily determine a state of eccentricity of the system.
In order to analyze an eccentricity state of, in particular, a lens system including multiple lens groups, such as a zoom lens, it is necessary to classify eccentricity into three eccentricity components consisting of a first one for the entire lens system, a second one for each lens group, and a third one for each lens element in each lens group and to determine how each eccentricity component is present with respect to the lens system in a design reference state. It is significantly difficult for one to determine and for displaying the details of the eccentricity of the lens system (e.g., the location of a tilted part, the position of a point of tilting, the degree and direction of tilting) by using only displayed numerical values from a result of measurement of eccentricity.